linux-kernel - Re: [PATCH v2 3/4] KVM: ioapic: extract body of kvm_ioapic_set

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Message-ID: <20140324175508.GA6143@potion.brq.redhat.com>
Date:	Mon, 24 Mar 2014 18:55:11 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, gleb@...nel.org,
	mtosatti@...hat.com, alex.williamson@...hat.com,
	jan.kiszka@...mens.com
Subject: Re: [PATCH v2 3/4] KVM: ioapic: extract body of kvm_ioapic_set_irq

2014-03-23 09:44+0100, Paolo Bonzini:
> Il 21/03/2014 19:58, Radim Krčmář ha scritto:
> >>> +	/*
> >>> +	 * Return 0 for coalesced interrupts; for edge-triggered interrupts,
> >>> +	 * this only happens if a previous edge has not been delivered due
> >>> +	 * do masking.  For level interrupts, the remote_irr field tells
> >          (^ to)
> >>> +	 * us if the interrupt is waiting for an EOI.
> >
> >How do we know we haven't delivered an edge-triggered interrupt when
> >ioapic_service() always clears this IRR bit?
> 
> We know we have at least delivered it to the local APIC(s).  If it
> is masked in the ioredirtbl, ioapic_service doesn't clear the IRR.

I see, LAPIC can't "refuse" an interrupt, so kvm_irq_delivery_to_apic()
won't (mustn't) fail. (The code looks fragile if it returned -1.)

Thanks.
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